[Programmed thymic T cell death and negative selection via Fas and TCR/CD3 complex].

In the immune system of thymic microenvironment, immature T cells are selected by T cell receptor (TCR)-mediated antigen stimulation and most of thymic T cells die by apoptosis. Molecular mechanism for the elimination of autoreactive T cells by apoptotic cell death in thymus is almost unknown, though a differential avidity model for TCR-mediated selection is recently proposed. On the other hand, Fas antigen (Fas), which is apoptosis inducing cell surface receptor, is expressed on antigen stimulated human thymocytes and involved in superantigen-induced negative selection. Recent studies have suggested that CD30 and CD40 ligand (gp39) on thymocytes is also involved in a part of negative selection. Thus, it is likely that the process of negative selection may involve multiple, and to some extent redundant, costimulation signals.